Proposed is an in vivo study of the transplacental flux of individual amino acids, glucose, and lactate in pregnant sheep. The effects of maternal fasting and maternal hormonal changes which occur during pregnancy or during fasting on transplacental flux of nutrients will be determined, and the subsequent effect of these changes on fetal growth assessed. The overall goal of this project is an understanding of the mechanisms by which maternal nutrition and endocrine status influence the provision of nutrients to the mammalian fetus to support appropriate growth. The specific objectives are: (1) to determine whether transplacental flux of amino acids is appreciably influenced by insulin, circulating concentrations of amino acids in maternal blood, or by the availability of other substrates for fetal nutrition; (2) to determine if the decreased uterine blood flow and decreased concentrations of glucose and other substrates in maternal blood which occur during fasting result in decreased umbilical amino acid uptake; (3) to detemine if placental lactogen and/or estrogens, the maternal serum concentrations of which increase during gestation, promote increased umbilical uptake of certain amino acids; (4) to assess whether there is independence or reciprocity which exists among umbilical uptakes of various substrates; and (5) to determine the relative effects of fetal substrate availability in fetal insulin and somatomedin levels on fetal cartilage growth.